Why does grass come in different lengths?

It's something I've always wondered, you know? I asked the man in the Post Office and he said: "Some grass does not get enough sun so stays short. Some grass gets too much sun and stays short. Other grass gets just enough sun and gets longer. Using Miracle Grow should also give you spectacular... show more It's something I've always wondered, you know?
I asked the man in the Post Office and he said:
"Some grass does not get enough sun so stays short. Some grass gets too much sun and stays short. Other grass gets just enough sun and gets longer. Using Miracle Grow should also give you spectacular growth. This principle also applies to human hair."

He gave me some diagrams to help a bit, but I still don't really understand.
http://i257.photobucket.com/albums/hh234...
24 answers 24